The invention relates to a pocket air velocity gauge wherein the air flows in through an inlet opening on the back of a housing into a ring channel disposed around a central pointer shaft. The channel extends over a center angle of approximately 360.degree. and the air leaves it through an outlet opening disposed at the end of the ring channel in a sidewall of the housing. An air vane disposed on a lever arm fastened to the pointer shaft, is arranged in the ring channel. The vane rotates counter to the action of a restoring spring connected to the pointer shaft, when it is struck by the inflowing air. The vane moves in the flow direction and hence a pointer connected to the vane is deflected a corresponding magnitude over a dial scale associated with the pointer.
In an older German patent application (P 34 11 432.7) a pocket wind velocity gauge of the above kind is described wherein the ring channel, disposed in a round housing, has the same cross section over its entire length and wherein the pointer restoring force is supplied by a single coil spring. The same is the case also in another wind velocity gauge (OS-PS 2 793 528), whose pointer deflection, however, is limited by respective limiting stops to an angle of about 110.degree., although the ring channel traversed by the air extends over almost 180.degree..
It is known that the flow pressure which leads to the deflection of the air vane or of the pointer is not directly proportional to the flow velocity of the air in the ring channel, but that this pressure exerted on the air vane is proportional at least approximately to the third power of the flow velocity, assuming constance of the approached surface. Due to this, it is not possible with the known wind velocity gauges to technologically realize a scale and a respective pointer deflection beyond an angle range greater than 110.degree.. Tests have shown that with such velocity gauges, beyond a pointer deflection of about 100.degree.-110.degree., measuring of air flow is no longer possible because, when this deflection angle is exceeded, the air vane with the pointer is abruptly rotated up to its stop.